Hydrocarbon conversion process

ABSTRACT

A hydrocarbon conversion process is disclosed which extends the useful life of a regenerable zeolite-containing hydrocarbon conversion catalyst. In one aspect of this process, a hydrocarbon feed containing fluorides is passed through a fluoride removal system which reduces the fluoride concentration of the feed to below 100 ppb. The hydrocarbon feed containing less than 100 ppb fluorine is then converted over a regenerable zeolite-containing hydrocarbon conversion catalyst. The zeolite-containing hydrocarbon conversion catalyst is regenerated with an oxygen-containing gas stream as necessary to burn off carbonaceous deposits on the catalyst so as to return the zeolite catalyst to a high level of activity.

CROSS REFERENCES TO RELATED APPLICATION

This application is a divisional application of prior copendingapplication Ser. No. 090,480, filed Aug. 28, 1987 now U.S. Pat. No.4,783,566.

BACKGROUND OF THE INVENTION

The present invention relates to an improved hydrocarbon conversionprocess which utilizes a regenerable zeolite-containing catalyst toprocess a hydrocarbon feed which has been treated to reduce the fluoridecontent therein to below 100 ppb.

It is a common practice in the hydrocarbon and petrochemical industry totreat feedstocks, products, and intermediates in order to purify streamsor to remove deleterious components from hydrocarbon streams.Hydrocarbon feedstocks and intermediate process streams are oftenpurified to increase process efficiency. That is, it is much moreefficient to process reactant hydrocarbons than it is to includerefractory hydrocarbons or hydrocarbons which lead to undesirableproducts in a catalyzed hydrocarbon process. Hydrocarbon reactionproducts are often purified or otherwise treated to enhance the productsvalue, stability, and so forth.

Additionally, impurities in hydrocarbons being processed in a catalyticsystem have been recognized as having a negative effect on catalyststability and conversion. For example, cracking catalysts are poisonedby metals such as nickel, vanadium, and sodium which originate in thehydrocarbon feed to a cracking unit. Treatment of such a feed to removeor passivate such metals is well known to increase the useful life ofcracking catalysts. In another example, sulfur accumulation on areforming catalyst promotes undesirable cracking reactions. Thetreatment of reformer feeds to remove sulfur components is a well knownmethod of maintaining process efficiency and protecting catalyststability.

In the case of a hydrocarbon conversion process utilizing a regenerablezeolite-containing catalyst, it is well known that regenerationprocedures which expose a zeolite-containing catalyst to steam severelyeffects the performance of the zeolite catalyst following regeneration.This performance loss, observed even under mild regeneration conditions,is typically not totally recoverable. Therefore, processes and methodsto suppress zeolite activity loss in a hydrocarbon conversion processemploying a regenerable zeolite are quite important in extending theuseful life and thus the economic viability of such a process.

It has now been surprisingly found that if a hydrocarbon feed is firsttreated to reduce its fluoride content to below 100 ppb that the use ofsuch a hydrocarbon feed in a hydrocarbon conversion process utilizing aregenerable zeolite will result in a higher retention of catalystactivity of the regenerated catalyst. The improvement being longercatalyst life expectancy because of the zeolite-containing catalystsgreater resistance to activity loss during catalyst regeneration.

OBJECTS AND EMBODIMENTS

A principal object of the present invention is to provide an improvedhydrocarbon conversion process which overcomes prior artzeolite-containing hydrocarbon conversion catalyst stability problems byrecognizing the high sensitivity of zeolite catalysts to fluorinecompounds by controlling the fluorine concentration of hydrocarbon feedsto such zeolite catalyzed processes to less than 100 ppb. Using such afeed in a process which employs a regenerable zeolite-containingcatalyst results in an extension of the useful life of thezeolite-containing catalyst. Accordingly, a broad embodiment of theprocess of the present invention is directed toward a hydrocarbonconversion process for catalytically converting a hydrocarbon containingfeed having a fluorine concentration of below 100 ppb in the presence ofa regenerable catalyst comprising a crystalline zeolite at hydrocarbonconversion conditions.

In another embodiment, a hydrocarbon conversion process is providedwhich utilizes the steps of: (a) subjecting a C₁ -C₁₀ hydrocarbon feedto a fluorine compound removal step to reduce the feed fluorine contentto below 100 ppb; (b) catalytically converting the fluorine-deficient C₁-C₁₀ hydrocarbon feedstock in the presence of a regenerable crystallinezeolite-containing hydrocarbon conversion catalyst where the crystallinezeolite has a silica to alumina ratio greater than 2; and, (c)regenerating the crystalline zeolite-containing hydrocarbon conversionwhich has become deactivated by the deposition of carbon in the form ofcoke upon the catalyst by exposing the deactivated catalyst to anoxygen-containing gas stream at conditions sufficient to combust thecoke and restore catalyst activity. The process described above isuseful in the conversion of C₁ to C₁₀ aliphatic hydrocarbon containingfeedstocks in hydrocarbon conversion processes such as paraffindehydrogenation, oligomerization, alkylation, aromatization,dehydrocyclodimerization, and the like.

In a preferred embodiment, the present invention is directed to animproved process for the dehydrocyclodimerization of a hydrocarbonfeedstock comprising C₂ to C₆ aliphatic components in the presence of aregenerable ZSM-type zeolite catalyst. The hydrocarbon feedstockinitially undergoes a fluorine compound removal step to reduce theconcentration of fluorine in the feed to below 100 ppb. The feedstockthusly treated is catalytically dehydrocyclodimerized in the presence ofa regenerable dehydrocyclodimerization catalyst comprised of a ZSM-typecrystalline zeolite. When deactivated by the accumulation ofcarbonaceous deposits known as coke on the catalyst, the catalyst isregenerated by exposing it to an oxygen-containing gas at conditionssufficient to combust the coke on the catalyst. Besides comprising aZSM-type zeolite component, the dehydrocyclodimerization catalystpreferably comprises a gallium component, a phosphorus-containingalumina component, and a refractory inorganic oxide component.

INFORMATION DISCLOSURE

The use of a crystalline zeolite in the catalysis of a hydrocarbonreaction is well known in the prior art. However, the improvement instability of a regenerable zeolite-containing catalyst when processing afluorine-deficient feed has not been fully recognized.

Methods for the removal of specific undesirable components fromhydrocarbon feeds prior to or following hydrocarbon conversion processare well known. The removal of selected components from a gas stream byadsorption is shown in U.S. Pat. No. 2,180,712. The increasedselectivity and surface area of molecular sieves has caused them topredominate in the removal of inorganic compounds from vapor streams. InChapter 16 of The Chemical Engineer's Handbook, 5th Edition, McGraw-HillBook Co., New York, 1973, the suitability of using alumina for dryinggases and the defluorination of alkylates is indicated on Page 16-5. Theuse of fixed-bed, continuous, and continuous countercurrent gas andliquid sorption operations are described starting at Page 16-23.Examples are presented using moving or fluidized beds of activatedcharcoal and silica gel for gas treating operations. U.S. Pat. No.3,775,310 presents a continuous ion exchange process usingcountercurrent flow of the adsorbent and treated liquid. The removal offluoride compounds specifically to increase zeolite-containinghydrocarbon conversion catalyst stability is however not believed to bedisclosed in any of these references.

U.S. Pat. No. 4,456,527 describes a hydrocarbon conversion process whichutilizes a hydrotreating step to reduce the sulfur content of a feed toa catalytic reforming process. The sulfur content of the feed is reducedto protect the stability of a catalyst comprising a large pore typezeolite containing at least one Group VIII type metal. The intent of the'527 patent is to protect and maintain the stability of azeolite-containing hydrocarbon conversion process. However, the '527patent discloses the advantages of feed sulfur removal and is completelysilent to the advantages of feed fluoride removal.

Surprisingly, many prior art patents disclose the use of a fluoridecomponent to modify different properties of a zeolite in azeolite-containing hydrocarbon conversion catalyst. U.S. Pat. No.3,594,331 discloses a method for increasing the thermal stability ofcrystalline zeolites by treating the zeolite with a dilute solution of afluorine compound. The treatment with a fluorine compound is a fluoridetreatment (column 3, line 41 et. seq.). After the fluoride treatment hasbeen completed, the zeolite (fluoride treated) incorporates 2 to 15grams of fluoride per 10,000 grams of zeolite. The patent does notehowever that excess fluoride actually decreases the thermal stability ofthe zeolite.

U.S. Pat. No. 3,933,983 discloses a fluoride treatment process similarto U.S. Pat. No. 3,594,331 except that an ion exchange step is added(see claim 1). Additionally, the removal of fluoride-containingcomponents within a zeolite with a soluble aluminum compound isdisclosed in Canadian Patent Number 1,218,348. The removal of fluoridecomponents is described as being desirable since the presence of suchinsoluble fluoride compounds in physical admixture with thealuminosilicate generally increases the rate of degradation of thealuminosilicates due to fluoride attack on the zeolite's lattice. Suchfluorides have a tendency to cause fluxing of inorganic materials underthermal or hydrothermal conditions which may destroy the zeolitesstructure. The prior art disclosures mentioned immediately aboveemphasize the fact that fluoride has been used advantageously to modifycatalyst properties during manufacture. The process of the instantinvention, unlike that of the '348 Canadian patent, treats fluorides inthe hydrocarbon feed by extracting them as opposed to removing fluoridesin a catalyst as a result of catalyst manufacture.

Zeolite-containing catalyst regeneration methods are also well known inthe prior art. Typically, the regeneration methods emphasize theimportance of performing the zeolite catalyst regeneration procedure atlow levels of moisture to reduce steam deactivation of the zeoliteduring regeneration procedures. Examples of such processes and methodsinclude removing combustion moisture with a water-lean adsorbent as isdone in U.S. Pat. No. 3,756,961, or by removing a portion of watercontaining gas from the system as is described in U.S. Pat. No.4,480,144. Many other methods of regenerating zeolite catalyst toprevent thermal degradation of the zeolite by steam are disclosed. Nonehave disclosed the advantages of regenerating a zeolite-containingcatalyst accrued by processing only hydrocarbon feed containing lessthan 100 ppb fluoride.

The prior art discloses various aspects of the instant invention such asfluoride removal methods, zeolite catalyst treating methods and catalystregeneration methods. However, no prior art disclosure describes ahydrocarbon conversion process such as described herein where aregenerable zeolitic catalyst's stability is improved by reacting itwith hydrocarbon feeds which have been treated so they contain onlyminute amounts of fluorides.

DESCRIPTION OF THE DRAWING

The drawing presents C₃ feed conversion results of pilot plant testingperformed on fresh and regenerated dehydrocyclodimerization catalysts asa function of hours-on-stream. The testing was performed usinghydrocarbon feedstocks containing 13,000 ppb, 500 ppb, and 0 ppb levelsof fluorine in the feed on zeolite-containing catalysts over a number ofregeneration cycles.

DETAILED DESCRIPTION

In its broadest aspect, the present invention consists of reacting ahydrocarbon containing feedstock of exceedingly low fluorine content(less than 100 ppb) over a zeolite-containing hydrocarbon conversioncatalyst where the zeolite-containing catalyst is regenerable. It hasbeen found, surprisingly and unexpectedly, that a zeolite catalystemployed in the instant process exhibits a higher level of activity uponregeneration than a zeolite catalyst of the prior art. This results in acatalytic process with a longer catalyst life expectancy. This improvedretention of catalytic activity after one or more regenerationprocedures increases the attractiveness of such a process by allowingthe catalyst of the instant invention to be regenerated more timesbefore zeolite catalyst replacement is required.

In accordance with the present invention, the process disclosed hereininvolves in part a hydrocarbon feed pretreatment step to reduce thelevel of fluoride components in a hydrocarbon feedstock to below 500ppb, and preferably to below 100 ppb based upon the weight of elementalfluorine in the treated hydrocarbon. The hydrocarbon is pretreatedbefore it is exposed to a regenerable zeolite-containing hydrocarbonconversion catalyst at hydrocarbon conversion conditions.

The terms "fluoride", "fluoride component", and/or "fluoride-containing"are used herein to describe any chemical formulation containingelemental fluorine alone or within its molecular structure. Thisincludes fluorine in its elemental and diatomic form and compoundscontaining fluorine atoms and atoms of other elements. Thehydrocarbon-containing process streams from which these materials areremoved may be characterized as fluid streams as they may be bothgaseous and liquid. In a refinery situation, it is anticipated thatfluoride-containing components may originate from fluoride-containingcatalysts such as boron trifluoride or aluminum fluoride, hydrogenfluoride, and the like, from a reactant used in a fluorination step, orfrom by-products of a hydrogen conversion reaction such asalkylfluorides produced as a by-product of an HF alkylation reaction.The previous description of potential sources of and types of fluoridecomponents in the hydrocarbon feed of the present invention is not meantto restrict the instant process. It is anticipated that hydrocarbonfeedstocks can become contaminated with fluoride components in arefinery in a myriad of methods. The method that a feedstock may becomecontaminated is not as important to this invention as is the treatmentand processing of such a contaminated feedstock.

A variety of methods are known in the art to remove fluoride componentsfrom gaseous and liquid hydrocarbon streams. One of the most commonmethods of removing these fluoride-containing chemicals is to pass thefluid stream through a bed of selective adsorbent such as alumina,bauxite, silica gel, or activated charcoal. This is normallyaccomplished using a fixed bed of the adsorbent, but moving beds havealso been utilized. For instance, alumina is used to removealkylfluorides from a liquid hydrocarbon stream. Such fixed bedadsorbent systems are commonly referred to as "guard beds" as theirpurpose as a fixed "bed" of adsorbent is to "guard" a reactor full ofexpensive catalyst from being contaminated with a catalyst deactivatorsuch as sulfur or, as in this case, fluoride components. It isanticipated that guard beds that are useful in removing fluorides fromhydrocarbon feedstocks of the present invention could contain anycompound, in solid, gel, or liquid that is known to scavenge fluoridecompounds. It is also anticipated that such a guard bed could manifestitself in any useful flowscheme known in the prior art. As mentionedabove, some useful adsorbents including alumina, activated charcoal, andsilica gel are all known to be useful guard bed adsorbents. In addition,zeolites, amorphous silica aluminas, crystalline silica, and the likecould all be usefully utilized in the instant process. It is anticipatedthat for ease of operation, a guard bed system would consist of twoparallel guard bed vessels, each containing a similar fluorideadsorptive material. Having two guard bed vessels will enable one guardbed vessel to be in operation while the other is not. In this way, acontinuous process can be maintained. It is also possible that distinctbeds of two or more adsorbents or intimate mixtures of two or morefluoride-scavenging adsorbents can be utilized in a fluoride guard bedof the instant invention. Methods of using liquids to remove halogencomponents, including fluoride components from hydrocarbon feeds arealso well known and documented. A basic aqueous solution works well inremoving most halogen-containing chemicals. U.S. Pat. No. 3,917,733describes a continuous process for treating a gaseous and a liquidhalogen-containing hydrocarbon stream simultaneously and continuously toreduce said halogen content of the hydrocarbon streams to low levels.The treatment described in the '733 patent is accomplished with aluminawhich becomes spent and is replaced on a continuous basis. Such aprocess also is capable of employing other fluoride-scavengingadsorbents besides alumina. A continuous process as described in the'733 patent or similar, or other continuous adsorbent processes known inthe prior art would be particularly advantageous as the fluoride removalstep of the instant process as a continuous fluoride removal step wouldresult in a more efficient overall process.

The above description of fluoride removal process which can be employedto remove fluorides from the hydrocarbon feed of the instant process hasbeen broad and brief. It is anticipated that any process utilizing anadsorbent, liquid, or some other known method to remove fluoride orfluoride-containing components from a gaseous or liquid hydrocarbon feedmay be successfully employed as a portion of the instant process. Infact, it is anticipated that a two-bed zeolite catalyst containinghydrocarbon conversion process could be successfully employed to removefluorides from a fluoride-containing hydrocarbon feed. Such a processwould utilize the crystalline aluminosilicate zeolite in the firstreactor as a sacrificial catalyst bed. The first reactor products couldbe separated to recover reactants or sent in entirety to a second orsubsequent reactor containing a crystalline aluminosilicate catalyst forfurther processing. The type of process would be characterized in thatthe fluoride content of the feed would be reduced to below 100 ppb inthe first zeolite catalyst containing reactor and processed insubsequent zeolite catalyst containing reactors. Whatever process isemployed to remove fluorides from a fluoride-containing hydrocarbon feedmust however be capable of reducing the fluoride content of the saidhydrocarbon to below 500 ppb and preferably to a level below 100 ppb.

The fluoride removal step can be useful on any hydrocarbon feedscontaining more than 100 ppb fluorides. However, due to the erection andoperational costs of a fluoride removal system, it is anticipated thatsuch a system will be most useful for removing fluorides fromfluoride-containing hydrocarbon feeds containing greater than 500 ppbfluorides.

The hydrocarbon conversion process disclosed as the process of thepresent invention comprises all hydrocarbon conversion processes whichemploy a regenerable zeolite-containing catalyst to accomplish a desiredhydrocarbon conversion reaction. Examples of such hydrocarbon conversionprocesses which have been disclosed as employing a regenerablezeolite-containing catalyst include among others, catalytic cracking,catalytic reforming, catalytic hydrotreating, alkylation of aromatic andaliphatic hydrocarbons, dehydrocyclodimerization, oligomerization,dehydrogenation, and so forth. It is anticipated that the desiredhydrocarbon conversion reaction can take place in the presence of aregenerable zeolite-containing catalyst in a reactor system comprising afixed bed system, a moving bed system, a fluidized bed system, or in abatch-type operation; however, in view of the fact that attrition lossesof the valuable regenerable zeolite-containing catalyst should beminimized and of the well-known operation advantages, it is preferred touse either a fixed bed catalytic system, or a dense phase moving bedsystem such as is shown in U.S. Pat. No. 3,725,249. It is alsoanticipated that the catalytic system may comprise a single regenerablecatalyst which has been formulated with a zeolite or a mixture of two ormore unique regenerable catalysts of which at least one has beenformulated with a zeolite component.

The zeolite component of the regenerable zeolite-containing hydrocarbonconversion catalyst may be any natural or synthetic zeolite known.Zeolitic materials are typically ordered, porous crystallinealuminosilicates having a definite crystalline structure as determinedby X-ray diffraction, within which there are a large number of smallercavities which may be interconnected by a number of still smallerchannels or pores. These cavities and pores are uniform in size within aspecific zeolitic material. Since the dimensions of these pores are suchas to accept for adsorption molecules of certain dimensions whilerejecting those of larger dimensions, these materials have come to beknown as "molecular sieves" and are utilized in a variety of ways totake advantage of these properties. Zeolites may be represented by theempirical formula:

    MnO.sub.2/n ·A1.sub.2 O.sub.3 ·xSiO.sub.2 ·yH.sub.2 O

in which n is the valence of M which is generally an element of Group Ior II, in particular, sodium, potassium, magnesium, calcium, strontium,or barium and x is generally equal to or greater than 2.

Prior art techniques have resulted in the formation of a great varietyof synthetic zeolites. The zeolites have come to be designated by letteror other convenient symbols, as illustrated by zeolite A (U.S. Pat. No.2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat.No. 3,110,007), zeolite ZK-5 (U.S. Pat. No. 3,247,195), zeolite ZK-4(U.S. Pat. No. 3,314,752), zeolite ZSM-5 (U.S. Pat. No. 3,702,886),zeolite ZSM-11 (U.S. Pat. No. 3,709,979), zeolite ZSM-12 (U.S. Pat. No.3,832,449), zeolite ZSM-20 (U.S. Pat. No. 3,972,983), zeolite ZSM-35(U.S. Pat. No. 4,016,245), zeolite ZSM-38 (U.S. Pat. No. 4,046,859), andzeolite ZSM-23 (U.S. Pat. No. 4,076,842), to name but a few.

The SiO₂ /Al.sub. O₃ ratio of a given zeolite is often variable. Forexample, zeolite X can be synthesized with SiO₂ /A1₂ O₃ ratios of from 2to 3; zeolite Y, from 3 to about 6. In some zeolites, the upper limit ofthe Si ratio is unbounded. ZSM-5 is one such example wherein the SiO₀ratio is at least 5 and up to infinity. U.S. Pat. No. 3,941,871 (Re. No.29,948) discloses a porous crystalline silicate made from a reactionmixture containing no deliberately added alumina in the recipe andexhibiting the X-ray diffraction pattern characteristic of ZSM-5 typezeolites. U.S. Pat. Nos. 4,061,724, 4,073,865, and 4,104,294 describecrystalline silicates or organosilicates of varying alumina and metalcontent.

In a preferred embodiment, the zeolite-containing catalyst of thepresent invention exhibits a silicon to alumina molar ratio of 2 ormore. The zeolites disclosed hereinabove as well as other knownsynthetic and naturally occurring zeolites which have a silicon toalumina molar ratio greater than 2 are all candidates as the preferredzeolitic component of the regenerable zeolite-containing hydrocarbonconversion catalyst of the instant invention.

It is an important aspect of the instant invention that thezeolite-containing hydrocarbon conversion catalyst be regenerable by theoxidation or burning of catalyst deactivating carbonaceous deposits withoxygen or an oxygen-containing gas. By "regenerable", it is meant thatat least a portion of the zeolite-containing catalyst's initial activitycan be recovered by combusting the coke deposits on the catalyst withoxygen or an oxygen-containing gas. The prior art is replete withzeolite catalyst regeneration techniques. Some of these regenerationtechniques involve chemical methods of increasing the activity ofdeactivated zeolites. Others are related to processes or methods forregenerating carbon (also known as coke) deactivated zeolites bycombustion of the coke with an oxygen-containing gas stream. Forexample, U.S. Pat. No. 2,391,327 (Mekler) discloses the regeneration ofcatalysts contaminated with carbonaceous deposits with a cyclic flow ofregeneration gases. U.S. Pat. No. 3,755,961 relates to the regenerationof coke-containing crystalline zeolite molecular sieves which have beenemployed in an absorptive hydrocarbon separation process. The processinvolves the continuous circulation of an inert gas containing aquantity of oxygen in a closed loop arrangement through the bed ofmolecular sieves. U.S. Pat. No. 4,480,144 relates to the use of acirculating gas to regenerate a coke deactivated zeolite-containingcatalyst. The circulating gas is maintained at a low moisture level bypurging wet gases from the loop while simultaneously introducing drygases to the loop. The conditions and methods at which azeolite-containing catalyst may be regenerated by coke combustion withoxygen vary. It is typically desired to perform the coke combustion atconditions of temperature, pressure, gas space velocity, etc. which areleast damaging thermally to the catalyst being regenerated. It is alsodesired to perform the regeneration in a timely manner to reduce processdown-time in the case of a fixed bed reactor system or equipment size inthe case of a continuous regeneration process.

Optimum regeneration conditions and methods are those typicallydisclosed in the prior art as mentioned hereinbefore. To reiterate,zeolite regeneration is typically accomplished at conditions including atemperature range of from 315° C. to 500° C. or higher, a pressure rangeof from atmospheric to 20 atmospheres, and a regeneration gas oxygencontent of from 0.1 to 23.0 mole percent. The oxygen content of theregeneration gas is typically increased during the course of a catalystregeneration procedure based on catalyst bed outlet temperatures inorder to regenerate the catalyst as quickly as possible while avoidingcatalyst-damaging process conditions.

The regeneration of zeolite catalysts is preferably conducted in twosteps, a main burn and a clean-up burn. The main burn constitutes theprincipal portion of the regeneration process. With the molecular oxygenlevel maintained below about 1.0 mole percent during this main burn, theburning of the coke consumes a major portion of the oxygen so thatmolecular oxygen in amounts less than that found at the reactor inlet isdetected in the gaseous stream at the outlet of the reactor vessel. Nearthe end of the main burn, oxygen consumption across the catalyst bedwill start to decrease producing an increasing concentration ofmolecular oxygen at the exit of the reactor. This point in the main burnis referred to as the oxygen breakthrough and essentially marks the endof the main burn. At this point, the clean-up burn portion of theregeneration is initiated by gradually increasing the molecular oxygenconcentration in the gas introduced to the catalyst bed. The oxygenconcentration can usually be slowly increased to about 7.0 mole percentor greater until the end of the clean-up burn which is indicated by agradual decline in the temperature at the exit of the catalyst bed untilthe inlet and outlet temperatures of the catalyst bed merge, i.e. thereis essentially no temperature rise across the bed.

U.S. Pat. No. 4,645,751 discloses a specific method of regenerating anoble metal containing zeolite catalyst. The method disclosed involves afirst coke-burning step followed by a second noble metal redispersingstep. It is anticipated that reactivation techniques such as the noblemetal redispersing technique taught in the '751 patent may be an aspectof the regeneration technique utilized in the practice of the presentinvention. Such reactivation techniques are utilized to restorecatalytic activity beyond that gained through zeolite catalyst cokecombustion methods alone. Another example of zeolitic catalyst activityreactivation techniques disclosed in the prior art is found in U.S. Pat.No. 4,649,127 which describes the use of a hydrogen contacting stepfollowed by a polar solvent contacting to reactivate nitrogen poisonedcatalysts. The regenerable zeolite hydrocarbon conversion catalystutilized in the instant invention must exhibit catalyst activityrecovery following a coke burning regeneration step. In addition to thecoke burning step, other methods of zeolite reactivation known in theprior art may be employed in the regeneration of the zeolite-containingcatalyst of the present invention to further enhance the activity of theregenerated catalyst.

It is a preferred embodiment of the hydrocarbon conversion process ofthe present invention that the hydrocarbon feedstock employed in theprocess is comprised of C₁ -C₁₀ aliphatic and aromatic hydrocarbons. Thehydrocarbon feedstock may contain minor amounts of larger carbon numberhydrocarbons and/or hydrocarbon feedstock diluents such as, but notlimited to, hydrogen, nitrogen, oxygen, carbon dioxide, steam, and soforth. It is also an aspect of the preferred process that the C₁ -C₁₀aliphatic and aromatic hydrocarbon feedstock may comprise a purecomponent selected from the C₁ -C₁₀ aliphatic and aromatic hydrocarbons,a mixture of two pure components such as ethane and ethylene and soforth up to and including a feedstock containing a mixture of many toall aliphatic and aromatic hydrocarbons. That is to say, a C₁ -C₁₀aliphatic and aromatic hydrocarbon feedstock may contain one or morealiphatic and aromatic hydrocarbon components. C₁ -C₁₀ phatic andaromatic hydrocarbons were chosen as the preferred feedstock for theinstant process for a variety of reasons. It was felt that C₁ -C₁₀hydrocarbons were the most likely to contain deleterious amounts offluoride components in the form of alkylfluorides. It was also felt thatprocesses employing such C₁ -C₁₀ hydrocarbon feedstocks such ascatalytic reforming, dehydrocyclodimerization, hydrogenation, and thelike are typically operated at reaction conditions which can causezeolite-containing catalysts to deactivate quickly by coke accumulationthereon resulting in frequent catalyst regeneration requirements.Therefore, the process of this invention is particularly suited toextending the viability of regenerable zeolite catalysts employed inhydrocarbon conversion processes utilizing a C₁ -C₁₀ aliphatic andaromatic hydrocarbon feedstock.

In preferred embodiments of the present invention, the desiredhydrocarbon conversion processes of the present invention aredehydrogenation, oligomerization, alkylation, anddehydrocyclodimerization.

Dehydrogenation is a well-known hydrocarbon conversion process.Dehydrogenation may be effected by reacting dehydrogenatablehydrocarbons in a dehydrogenation process at dehydrogenation conditionsin the presence of certain zeolite-containing catalytic compositions ofmatter. The particular dehydrogenation catalysts which are employed arewell known in the art and comprise such compounds as nickel, and iron,and the like composited on a solid zeolite-containing support. Somedehydrogenation processes have employed, in addition to thedehydrogenation catalysts, an oxidation catalyst in the reactionprocess. The presence of the oxidation catalyst is precipitated by thefact that it is advantageous to oxidize the hydrogen which is producedby contact with an oxygen-containing gas in order to maintain thedesired reaction temperature and reaction equilibrium. For example,styrene, which is an important chemical compound utilized for thepreparation of polystyrene, plastics, resins or synthetic elastomerssuch as styrene-butadiene rubber, etc., may be prepared from thedehydrogenation of ethylbenzene. A variety of dehydrogenatablehydrocarbons are also C₁ -C₁₀ aliphatic and aromatic hydrocarbons.Examples of such hydrocarbons which are susceptible to dehydrogenationin a dehydrogenation process utilizing known zeolite-containingdehydrogenation catalysts include lower alkl-subsytituted aromatichydrocarbons such as ethylbenzene, diethylbenzene, isopropylbenzene,o-ethyltoluene, m-ethyltoluene, p-ethyltoluene, o-isopropyltoluene,m-isopropyltoluene, p-isopropyltoluene, ethylnaphthalene,propylnaphthalene, isopropylnaphthalene, diethylnaphthalene, etc.;paraffins such as ethane, propane, n-butane, isobutane, n-pentane,isopentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, andbranched chain isomers thereof; cycloparaffins such as cyclobutane,cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane,ethylcyclopentane; olefins such as ethylene, propylene, 1-butene,2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, 3-hexene, andbranched chain derivatives thereof, etc. It is intended to include anyzeolite-containing dehydrogenation catalyst disclosed in the prior artas a regenerable zeolite-containing catalyst of a preferreddehydrogenation conversion process of the present invention. Thedehydrogenation of dehydrogenatable hydrocarbons such as, for example,ethylbenzene, propane, or ethane is effected by contacting the desireddehydrogenatable hydrocarbon with the aforesaid regenerablezeolite-containing hydrocarbon conversion catalyst. Dehydrogenationconversion conditions typically are in the range of from 350° C. toabout 750° C. and at reaction pressures ranging from about 0.1 to about20 atmospheres. The exact dehydrogenation conditions are, however, afunction of the particular hydrocarbon undergoing dehydrogenation. Otherreaction conditions will include a Liquid Hourly Space Velocity based onthe hydrocarbon charge of from about 0.1 to about 20 hr-1 Diluents suchas steam, hydrogen, oxygen, nitrogen, and the like may be added to thefeed or at any point in the reactor. The number of reactors or catalystbeds utilized in the dehydrogenation reaction zone may be one or morethan one, and as previously mentioned, the dehydrogenation catalyst maybe employed in conjunction with an oxidation catalyst to increaseprocess efficiency. The above description of dehydrogenation processingconditions and methods is meant to be exemplary in nature and is notmeant to restrict the possible dehydrogenation process schemes able tobe practiced within the scope of this invention.

A second preferred hydrocarbon conversion process of the instantinvention is oligomerization. The oligomerization process is well knownin the prior art. In a brief description, the oligomerization processcomprises uniting hydrocarbon olefins into larger olefinic hydrocarbonmolecules consisting of multiples of the original molecules. Therefore,the oligomerization of, for example, ethylene (C₂.sup.═) would produceC₄, C₆, and perhaps C₈ olefins or dimers, trimers, and tetramers of theoriginal ethylene feed molecule. In the case of a mixed light olefinfeed, combinations of dimers, trimers, and perhaps tetramers and morehighly substituted molecules comprising a mixture of the mixed feedolefins would be produced. In general, the feedstock to anoligomerization reactor might comprise one or a mixture of two or moreolefins containing from 2 to 10 carbon atoms, and preferably containingfrom 2 to about 6 carbon atoms such as ethylene, propylene, butene-1,butene-2, pentene-1, pentene-2, and pentene-3. Oligomerization may thenbe effected by reacting the olefin in the presence of azeolite-containing catalyst at oligomerization conditions which includesa temperature in the range of from about -20° C. to about 120° C., thepreferred range being from about 30° C. to about 80° C., and a pressurein the range of from about 5 to about 68 atmospheres. The pressure whichis utilized may be the autogenous pressure provided for by. thefeedstock, if in gaseous phase, or, the feedstock may supply only apartial pressure, the remainder of such pressure being provided by theintroduction of an inert gas such as nitrogen, helium, argon, etc. intothe reaction zone. As stated hereinabove, the products of theoligomerization reaction comprise mainly dimers, trimers, and tetramersof the original olefinic reactant or reactants. Such oligomerizationproducts are useful in further processing such as in the production oflinear alkylbenzenes, and as a motor fuel constituent among other uses.It is of course an important aspect of the present invention that theoligomerization reaction take place in the presence of a regenerablezeolite-containing catalyst utilizing a feed that has been pretreated toreduce the fluoride content therein to below 100 ppb. It is also anaspect of the preferred oligomerization process that the zeolite have asilicon to aluminum molar ratio of 2 or more and that thezeolite-containing catalyst is regenerable by combustion of coke thereonwith an oxygen-containing gas at regeneration conditions.

Alkylation is a third preferred hydrocarbon conversion process of theinstant invention. Motor fuel alkylation and aromatic alkylationutilizing a zeolite catalyst comprise some of the various types ofalkylation processes which can be accomplished utilizing a C₁ -C₁₀aliphatic and aromatic hydrocarbon feedstock which has been firsttreated to reduce the fluoride content therein to less than 100 ppb.Motor fuel alkylation is achieved as a result of the reaction between anisoparaffin and an olefin. The motor fuel alKylate product isparticularly useful as a high octane blending stock in gasoline. The useof a crystalline aluminosilicate was disclosed in U.S. Pat. No.3,251,902 among others as an effective motor fuel alkylation catalyst.The alkylation of aromatics such as benzene with olefins such asethylene, propylene, and so forth is also well known in the prior artfor producing such useful aromatic products as ethylbenzene and cumeneto mention but a few. Such products are useful as plastic precursors, asfeedstock for other petrochemical processes and so forth. Processingschemes and conditions useful in various alkylation reactions varywidely depending upon feedstock, catalyst, whether the reaction is gasphase or liquid phase, and so on. The use of a zeolite-containingregenerable alkylation catalyst in a process for the alkylation of anolefin with a paraffin while not common is disclosed in the prior artsuch as in U.S. Pat. No. 3,778,489. Conditions suitable for thealkylation of such a feedstock in the presence of a zeolite-containingcatalyst include a temperature of from -60° C. to 100° C., a pressure offrom 1 to 20 atmospheres, an olefin to paraffin molar feed ratio of from1:1 to 1:20, and a liquid hourly space velocity of from 0.1 to 20.

The use of zeolite-containing catalysts in the alkylation of aromatichydrocarbons is well known and documented such as in U.S. Pat. No.4,185,040 which describes a crystalline aluminosilicate zeolite catalystand its usefulness in the alkylation of an aromatic with a C₂ -C₄olefin. Process conditions sufficient to promote the alkylation of anaromatic such as benzene with a C₂ -C₄ olefin in the presence of aregenerable zeolite-containing catalyst include a temperature of from80° C. to 400° C., a pressure of from 1 to 40 atmospheres, an aromaticto olefin mole ratio of from 1:1 to 20:1, and a liquid hourly spacevelocity of from 0.1 to 20. Process flow schemes, process combinations,the use of cofeeds, etc. are all applicable to the aromatic alkylationconversion process of the present invention. It is therefore an aspectof the preferred alkylation conversion process of the instant inventionthat the alkylation reaction be performed at any conditions and usingany method disclosed in the prior art which utilizes a regenerablezeolite-containing catalyst.

Dehydrocyclodimerization is the final preferred process of the presentinvention. Dehydrocyclodimerization is a process utilizing reactantscomprising paraffins and olefins, containing from 2 to 6 carbon atomsper molecule. These reactants are reacted over a catalyst to produceprimarily aromatics. H₂ and light ends as by-products. Typically, thedehydrocyclodimerization reaction is carried out at temperatures inexcess of 260° C. using dual functional catalysts containing acidic anddehydrogenation components. These catalysts include crystallinealuminosilicate zeolites which have been successfully employed ascatalyst components for the dehydrocyclodimerization reaction.

Many regenerable zeolite-containing catalysts have been disclosed in theprior art as useful for the dehydrocyclodimerization of C₂ -C₆ aliphatichydrocarbons. These catalysts as well as processes employing suchcatalysts are disclosed as potential catalysts and processing schemes ofthe preferred dehydroclodimerization process of the present invention.

It is most preferred that the hydrocarbon conversion process of theinstant invention comprise first subjecting a C₂ -C₆ aliphatichydrocarbon feedstock to a fluoride removal step to reduce theconcentration of fluoride in said feed to below 100 ppb. The treatedfeed is then contacted with a ZSM-type zeolite-containing catalyst in adehydrocyclodimerization reaction zone at dehydrocyclodimerizationconditions followed by regeneration of the coke deactivated zeolitecatalyst in the presence of an oxygen-containing gas. The ZSM zeolitecomponent of the preferred dehydrocyclodimerization catalyst ispreferably ZSM-5. The dehydroc.yclodimerization catalyst preferablycontains, in addition to a ZSM-5 zeolite component, from 0.1 to 5 wt. %of a gallium component, and from 30 to 70 wt. % of aphosphorus-containing alumina component. It is also preferred that thephosphorus to alumina ratio of the phosphorus-containing alumina rangesfrom 1:1 to 100. U.S. Pat. No. 4,636,483 describes the preferreddehydrocyclodimerization catalyst and is incorporated herein byreference.

It has not been intended through the description of the four preferredhydrocarbon conversion processes hereinabove to limit the hydrocarbonconversion aspect of the process of the present invention. As previouslystated, the instant process will be useful in hydrocarbon conversionprocesses which utilize a regenerable zeolite to maintain regeneratedzeolite-containing catalyst activity by first treating said hydrocarbonfeed to reduce the fluoride content therein to below 500 ppb andpreferably below 100 ppb. Additionally, it is not intended to limit thescope of the preferred hydrocarbon conversion processes useful in theinstant process by the generic description of said processes givenabove. The only limitation placed on said processes is that thefeedstock useful in such preferred processes must be limited at most toC₁ -C₁₀ aliphatic and aromatic hydrocarbons, that catalysts useful insaid processes must be regenerable by coke combustion and that thecatalyst must contain a zeolite with a silicon to alumina molar ratiogreater than 2. It is left up to the prior art to limit the scope ofhydrocarbon conversion processes useful in the instant invention basedupon the limitations set forth herein.

It is an aspect of this invention that the hydrocarbon conversionprocess be a complete process. That is to say, the hydrocarbonconversion process will comprise a reaction section and other sectionssuch as gas recycle, liquid recycle, product recovery, and the like suchthat the process is viable and efficient. Examples of some of theproduct recovery techniques that could be employed alone or incombination in the product recovery zone of a hydrocarbon conversionprocess are: distillation including vacuum, atmospheric, andsuperatmospheric distillation; extraction techniques including, forexample, liquid/liquid extractions, vapor/liquid extractions,supercritical extractions and others; absorption techniques, adsorptiontechniques, and any other known mass transfer techniques which canachieve the recovery of the desired products.

The following examples will serve to illustrate certain specificembodiments of the herein disclosed invention. The examples should not,however, be construed as limiting the scope of the invention as setforth in the claims as there are many variations which may be madethereon without departing from the spirit of the invention, as those ofskill in the art will recognize.

EXAMPLE I

This example introduces methods used for preparing and/or determiningthe fluoride content of fluoride-containing light hydrocarbonfeedstocks. Three propane feedstocks prepared and/or evaluated utilizingthe method as set forth herein below were subsequently tested in ExampleII.

The first propane feedstock was analyzed directly and determined tocontain 13 ppm (13,000 ppb) fluoride therein. A spectrophotometricanalysis was used to determine the propane fluoride content. The methodused consisted of first burning a known weight of propane feed with astainless steel burner in a Wickbold quartz-tube oxy-hydrogen combustionapparatus. The combustion products were absorbed in a 25 ml solution of2% boric acid that had been subsequently diluted with water from anapparatus cleaning step. The solution was then treated with 5 ml offormaldehyde to remove excess peroxides and heated until 70 ml ofsolution remain. The 70 ml of fluoride-containing solution was thendiluted to 100 ml. It was necessary to determine the proper aliquotempirically from a dilution of the diluted absorber solution containingno fluoride reagent. 40 ml of water and 10 ml of a fluoride reagentprepared by mixing equal volumes of a solution of 2.87 g SPADNS EastmanKodak 7309(4-5-dihydroxy-3-(p-sulfophenylazo)-2,7-naphthalene-disulfonic acid,trisodium salt) in 500 ml water and a zirconyl chloride solutioncomprising 0.133 g zirconyl chloride, 350 ml conc HCl diluted to 500 mlwere added to a 100-ml volumetric flask. Using a Mohr pipet, 0.2 ml ofthe diluted absorber solution was transferred to the flask containingwater and fluoride reagent and the degree of bleaching of the fluoridereagent was noted. Diluted absorber solution was added to the reagentflask in 0.2 ml increments until a suitable degree of bleaching wasobtained. The final solution was diluted to the 100 ml mark with water,mixed well, and the fluoride concentration was determined from aprepared calibration curve based upon the volume of absorber solutionused.

The fluoride contents of the propane feeds containing 500 ppb andessentially 0 ppb fluorides were determined in a different manner. Inboth cases, the propane feed was pretreated by passing the feed across aguard bed containing a gamma-alumina adsorbent at 230° C. and at from13.6 to 17.0 atmospheres. The guard bed was replaced and the aluminaanalyzed for fluorides until, in the case of the second feedstock, atrace of fluoride was found on the guard bed alumina and, in the case ofthe third feedstock, no fluorides were detected on the alumina. Thesecond and third feedstocks were then processed in the pilot plant perthe procedure established in Example II and a representative sample ofthe spent catalyst from Example II was then analyzed for fluoride. Fromthe spent catalyst fluoride analysis, and based upon the weight of feedprocessed, it was determined that the feedstock prepared for the secondseries of tests contained at least 500 ppb fluoride and the feedstockprepared for the third series of tests was essentially fluoride-free.

EXAMPLE II

In order to demonstrate the retention of catalytic activity of aregenerable zeolite-containing catalyst when processing a feedstockcontaining less than 100 ppb of fluorine, a hydrocarbon conversioncatalyst disclosed in U.S. Pat. No. 4,636,483 was prepared by the methodset forth below. A first solution was prepared by adding phosphoric acidto an aqueous solution of hexamethylenetetramine (HMT) in an amount toyield a phosphorus content of the finished catalyst equal to about 11wt. %. A second solution was prepared by adding a ZSM-5 type zeolite toenough alumina sol, prepared by digesting metallic aluminum inhydrochloric acid, to yield a zeolite content in the finished catalystequal to about 67 wt. %. These two solutions were commingled to achievea homogeneous admixture of HMT, phosphorus, alumina sol, and zeolite.This admixture was dispersed as droplets into an oil bath maintained atabout 93° C. The droplets remained in the oil bath until they set andformed hydrogel spheres. These spheres were removed from the oil bath,water washed, air dried, and calcined at a temperature of about 482° C.A solution of gallium nitrate was utilized to impregnate the spheres toachieve a gallium content on the finished catalyst equal to about 1 wt.%. After impregnation, the spheres were calcined a second time, in thepresence of steam, at a temperature of about 649° C.

The hydrocarbon conversion catalyst as prepared above was utilized in adehydrocyclodimerization pilot plant to convert a propane feed intoaromatics. Three series of tests were performed. Each series wasperformed with a feedstock containing different amounts of fluoride.Each cycle consisted of a pilot plant conversion run lasting about 100hours, followed by a catalyst regeneration step. The amounts of fluorinein the feed were 13,000 ppb, 500 ppb, and essentially 0 ppb for series1, 2, and 3, respectively. The zeolite-containing catalyst was exposedto the propane feedstock and tested for dehydrocyclodimerizationperformance in identically the same manner in all series and cyclesusing a flow reactor processing a feed comprising 100% propane andvarying levels of fluoride. The operating conditions used in theperformance test comprised a reactor pressure of 1 atmosphere, a liquidhourly space velocity of 0.8 hr⁻¹, and a reaction zone inlet temperatureof about 538° C. The change in the conversion of the feed over 100 hoursof processing was monitored.

Following each pilot plant run, the same catalyst was regenerated andrerun for approximately 100 hours while processing a feedstock with thesame level of fluoride. This testing was repeated for four or five timesfor each test series, with each pilot plant run of the catalystcomprising one cycle in the series.

The catalyst regeneration method was similar in all cases. The procedureconsisted of placing the coke deactivated zeolite-containing catalyst ina 0.28 meter (11-inch) bed and establishing an inert gas flow across thecatalyst bed at a gas hourly space velocity of 4800 hr⁻¹. Thecorresponding superficial velocity was 0.5 m/sec (1.6 ft/sec) and theregeneration was performed at atmospheric pressure. The regenerationtemperature and oxygen content were varied over the 7-hour regenerationbased upon the schedule below:

    ______________________________________                                        Hours        Temp. (°C.)                                                                       O.sub.2, mole %                                       ______________________________________                                        0-1          490        1                                                     1-2          490        2                                                     2-3          490        5                                                     3-4          490        20                                                    4-5          490-540    20                                                    5-7          540        20                                                    ______________________________________                                    

After regeneration, the catalyst was cooled and then reloaded into thedehydrocyclodimerization pilot plant for another cycle of testing. Eachcycle is counted upon the completion of a pilot plant run. Thus, thepilot plant testing of the fresh catalyst would be cycle number 1. Afour-cycle catalyst will have undergone three regenerations.

The surprising pilot plant results of the series of tests can be foundin the attached FIGURE. The FIGURE is a plot of C₃ conversion over timein the pilot plant. First and last cycle pilot plant conversion resultsare plotted for each of the series of three tests. Before discussing theresults, it should be noted that the initial cycle results using a freshcatalyst in each of the three series were essentially identical. Thisresult indicates that the pilot plant test results are reproducible. Thefirst series utilized a C₃ feedstock containing 13 ppm of fluorine.After four cycles in which three catalyst regeneration steps had beenperformed, the catalyst lost 12% of its original C₃ conversion ability.The second series utilized a C₃ feedstock containing 500 ppb fluorine.After five cycles in which four catalyst regeneration steps had beenperformed, the catalyst lost about 6% of its original C₃ conversionability. The final series, series 3, utilizing an essentiallyfluorine-free C₃ feed exhibited no loss of C₃ conversion over fivecycles of testing including four regenerations.

It can be readily seen from these results that the removal of fluorinecompounds from a hydrocarbon feedstock and the processing of such afeedstock containing very low levels of fluorine is highly desirable inmaintaining the activity of a zeolite-containing regenerable hydrocarbonconversion catalyst. The presence of even small amounts (500 ppb) offluorides caused appreciable catalyst activity loss after only fourregenerations, thus providing the impetus for removing as muchdetrimental fluorides from the feed as possible.

What is claimed is:
 1. A hydrocarbon conversion process selected fromthe group consisting of dehydrogenation, oligomerization, and alkylationcomprising reducing the fluoride content of a fluoride-containinghydrocarbon feed to below 100 ppb and catalytically converting thehydrocarbon feed in the presence of a catalyst comprising a regenerablecrystalline zeolite at hydrocarbon conversion conditions where thecrystalline zeolite catalyst is regenerated by a procedure whichcomprises the combustion of carbonaceous material thereon with anoxygen-containing gas.
 2. The hydrocarbon conversion process of claim 1further characterized in that the crystalline zeolite catalyst has asilicon/aluminum molar ratio of 2 or more.
 3. A hydrocarbon conversionprocess selected from the group consisting of dehydrogenation,oligomerization, and alkylation comprising the steps of:(a) subjecting afluoride-containing hydrocarbon feed comprising C₁ -C₁₀ hydrocarbons toa fluoride removal step and reducing the concentration of fluorine insaid fluoride-containing hydrocarbon feed to below 100 ppb; (b)catalytically converting the hydrocarbon feed having a fluorideconcentration of below 100 ppb in the presence of a regenerablehydrocarbon conversion catalyst comprising a crystalline zeolite with asilica/aluminum molar ratio of greater than 2; and (c) regenerating theregenerable hydrocarbon conversion catalyst which has become deactivatedby deposition of carbonaceous material thereon by a procedure whichcomprises exposing said deactivated catalyst to an oxygen-containing gasstream at regeneration conditions.
 4. The hydrocarbon conversion processof claim 3 further characterized in that the crystalline aluminosilicatezeolite component of the hydrocarbon conversion catalyst is ZSM-5. 5.The hydrocarbon conversion process of claim 3 further characterized inthat the fluoride removal step comprises a guard bed containing afluorine component absorptive compound.
 6. The dehydrocyclodimerizationprocess of claim 3 further characterized in that the fluoride removalstep comprises the use of a non-regenerative adsorbent in a continuousprocess.